The invention relates to heating devices, and particularly, to gas heating devices. More particularly, the invention relates to control of gas heating devices.
Gas-fired heating devices such as water heaters often include a combustion chamber and air plenum disposed below a water tank. A gas manifold tube, an ignition source, a thermocouple, and a pilot tube typically extend into the combustion chamber. When the temperature of the water in the tank falls below a set minimum, gas fuel is introduced into the combustion chamber through the gas manifold tube and a burner element. This gas fuel is ignited by a pilot flame or the ignition source, and the flame is maintained around the burner element. Air is drawn into the plenum via an air inlet, and mixes with the gas fuel to support combustion within the combustion chamber. The products of combustion typically flow through a flue or heat exchange tube in the water tank to heat the water by conduction.
These gas-fired heating devices are often subjected to abnormal combustion conditions. For example, some water heaters are often positioned in areas that are also occupied by other equipment that has a gasoline-powered internal combustion engine. In such cases, it is not uncommon that there be gasoline and other flammable substances (e.g., kerosene, diesel, turpentine, solvents, alcohol, propane, methane, and butane) present in the same area. Such flammable substances often emit flammable vapors. Other foreign objects in the areas such as lint, dust, and oil (“LDO”) can also be introduced to the air inlet during the combustion. The foreign objects will accumulate and eventually block portions of the air inlet. A blocked air inlet can reduce the amount of air needed for stoichiometric combustion.